This invention relates to an article including a member that, during operation, includes a portion subject to tensile stress of an amount that can result in cracking of the member. More particularly, the invention relates to a turbine engine component including a wall having a portion subject to low cycle fatigue (LCF) cracking from tensile stress during operation.
Gas turbine engines generally include nozzles, for example turbine nozzles, including a plurality of spaced-apart stationary airfoil shaped vanes supported between generally circumferentially disposed band type members, sometimes referred to as shrouds or shroud segments. One example of such a structure is described in U.S. Pat. No. 5,343,694--Toborg et al. (patented Sep. 6, 1994). An inner surface of such a band or shroud segment is exposed to the flow of fluid under pressure, for example pressurized gas including air and products of combustion. Efficiency of the engine is based, in part, on the avoidance of leakage of such pressurized fluid out of the fluid stream.
In some gas turbine engine designs, it has been observed that certain portions of such a band, particularly on the flowpath side of a turbine nozzle vane or vane segment, during operation are under a relatively high amount of tensile type of stress. During cyclic operation of the engine, such tensile stress results from a cyclic type of bending of the band, sometimes referred to as chording. For example, such high tensile stress portions have been observed in the band in the vicinity of vane leading edges, trailing edges, or both. The relatively high amount of tensile stress can be sufficiently high to result, during operation, in the formation of a LCF crack in the band. At the same time, other, adjacent portions of the same band are in compression or under a tensile stress in an amount less than that which would result in LCF cracking. The LCF crack in the band extends from the high tensile stress portion of the band generally toward, and stops at, the band portion under compressive stress or lower tensile stress.
It has been a practice to repair such cracks by methods including one or a combination of welding, diffusion bonding (some forms of which are referred to as Activated Diffusion Healing), brazing, etc. However, such repair methods can be relatively temporary as well as time consuming and expensive. Sometimes attempts to repair such a crack in a component are unsuccessful, resulting in scrapping of the component. Preparation of new components to avoid such cracking as well as a crack repair of operated components, resulting in a restructured article and that extends the operating life of an article requiring less frequent repair, is highly desirable.